Frictional properties of actinolite-chlorite gouge at hydrothermal conditions

Ayumi S. Okamoto, André R. Niemeijer, Toru Takeshita, Berend A. Verberne*, Christopher J. Spiers

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Exhumed subduction zones frequently show widespread actinolite-chlorite (Act-Chl) dominated compositions, suggesting that this may play an important role in controlling megathrust fault slip. We investigate the frictional behavior of simulated Act-Chl (85:15) gouge mixtures derived from natural mafic metamorphic rocks, under hydrothermal conditions using a ring shear deformation apparatus. Experiments were performed at effective normal stresses (σn eff) of 50–200 MPa, pore fluid pressures (Pf) of 50–200 MPa, at temperatures (T) of 23–600 °C. In each experiment we applied a shear displacement (x) of ~10 mm at a constant sliding velocity (v) of 10 μm/s, followed by v-stepping in the range 0.3–100 μm/s, and slide-hold-slide (SHS) tests with hold times (t) ranging from 3 s to 3000 s. We quantified the rate- and state-dependent friction parameter (a-b), and investigated the effect of t on fault healing (Δμpk). The results showed no effects of temperature on the coefficient of friction (μ ≈ 0.6–0.7), or on (a-b), with some experiments showing persistent, displacement-hardening or -weakening trends. Nonetheless, effects of v and of normal stress (σn = σn eff + Pf) on (a-b) fall into three temperature regimes: (1) T = 23–100 °C, (2) T = 200–400 °C, and (3) T = 500–600 °C. In Regimes (1) and (3), (a-b) > 0 for all conditions tested, whereas in Regime (2), (a-b) ≤ 0, at σn eff = Pf = 50 MPa and v = 0.3–3 μm/s. We discuss on the origin of persistent displacement-hardening or -weakening trends observed, and assess the implications of our data for subduction zone seismogenesis. Extrapolation of (a-b)-data using multiple linear regression suggests that high pore pressure ratios (>0.9) are needed to promote seismogenesis in faults cutting actinolite-chlorite compositions.

Original languageEnglish
Article number228377
Number of pages15
JournalTectonophysics
Volume779
DOIs
Publication statusPublished - 20 Mar 2020

Funding

We thank Tony van der Gon-Netscher, Gert Kastelein, Eimert de Graaff and Peter van Krieken for technical support, and Ichiko Shimizu for fruitful discussions. The first author thanks S. den Hartog for her advice when using the ring shear apparatus at Utrecht University. Changrong He and Brett Carpenter are thanked for constructive reviews which improved the final manuscript. This study was funded by JSPS KAKENHI grant # 13J03294 awarded to ASO. ARN was supported by the Netherlands Organisation for Scientific Research (NWO) through VIDI grant nr. 854.12.011 and by ERC starting grant SEISMIC (nr. 335915). TT was supported by JSPS KAKENHI grant #26109004, and BAV by JSPS KAKENHI grant #19K14823.

Keywords

  • Actinolite
  • Chlorite
  • Earthquake
  • Friction
  • Megathrust
  • Subduction

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